Although metabolic alterations in tumors were first described nearly a century ago, it has only been within the last decade that changes in the activity of metabolic enzymes have been directly linked to tumorigenesis. Isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2), the enzymes responsible for the NADP+- dependent conversion of isocitrate (ICT) to ?-ketoglutarate (?KG), are mutated in over 80% of adult grade II and grade III gliomas and secondary glioblastomas, and up to 20% of acute myeloid leukemias. Intriguingly, many IDH mutations may serve as both tumor suppressors and oncogenes; all mutations characterized to date result in significant deficiency in ICT turnover, but surprisingly, many also gain a novel neomorphic activity. Instead of the normal oxidative decarboxylation, many IDH mutants catalyze the NADPH-dependent reduction of ?KG to the proposed oncometabolite, 2-hydroxyglutarate (2HG). This proposal seeks to elucidate the catalytic pathway and structural features of tumorigenic IDH mutations to elucidate the molecular mechanisms of dysfunction that support oncogenesis using pre-steady-state kinetics, biophysical methods, X-ray crystallography, microspectrophotometry, and cellular assays. This will clarify the contributions of deficient normal activity and neomorphic activity in enzymatic dysfunction, and how structural alterations influence these contributions. Further, the potential for IDH mutations to cause oxidative stress will be explored to identify important tumorigenic pathways. Such studies provide a critical foundation to aid the design of effective IDH-targeted therapy, and to help predict which mutations in patients will likely be amenable to such treatment. The long-term career goal is to establish an independent academic research program examining the molecular mechanisms of enzymatic dysfunction in metabolic enzymes, and how these mechanisms contribute to oncogenesis. To achieve this, two major short-term goals include gaining the significant training required to complete the aims of the project, and receiving career development mentoring. An advisory committee of experts of many of the techniques proposed has been assembled to assist in experimental training and data analysis and to provide mentorship in career development. This will supplement the vital mentoring and training provided by the postdoctoral mentor. Further support will come from collaborators, who are experts in the remaining techniques described in this proposal. Attendance at career development workshops and seminars at Yale University, and at courses at Yale University, the Brookhaven National Laboratory, and Cold Spring Harbor will provide required training and development. Finally, opportunities for manuscript preparation, grant writing, mentoring students, giving talks, and presenting at conferences will further support the long term goal of leading a successful independent research program. By gaining experimental training and seeking out opportunities for career development, I will acquire the tools necessary to develop an independent research program exploring the molecular mechanisms of defects in cancer metabolism.